Understanding the source code

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This document is a guided tour through Terminologue's code base. The goal is to help you understand how Terminologue works inside so that you can diagnose issues, fix bugs and help with developing Terminologue further.

What awaits you inside

As you probably know by now, Terminologue's backend is written in Node.js, which means it's all server-side JavaScript. In addition to Node.js itself, Terminologue makes use of the Express framework. Express is a small framework which helps us to set up the various URL end-points on the server and which tells Node.js what should happen when a user hits one of those end-points. If you are familiar with Node.js and Express, you will find everything here very easy to understand. If you are not but if you do know some other web development technology, we think you will still be able to follow at least the principles of what we're saying in this document.

When Terminologue sends web pages to the client it formats them using a templating engine called EJS. The syntax of EJS is similar to ASP and ASP.NET: server-side code is surrounded by <% and %>, the rest is normal HTML.

The client-side bits of Terminologue are written in "almost pure" HTML, JavaScript and CSS. By "almost pure" we mean that we don't use any "all-inclusive" frameworks and that we don't use anything that would require post-processing or compilation before being served to the client. We do however use a set of client-side scripts and stylesheets called Screenful which gives us much of the client-side functionality. Most of the web pages the user sees in Terminologue are one-page applications: the web page is served to the browser and then, as the user interacts with various on-screen widgets, Screenful sends AJAX requests to the server and receives responses back from it. All data flowing between the client and server is in JSON.

JSON is also the format in which data is stored internally in databases on the server. For backend storage Terminologue uses SQLite which is a file-based database engine. Every database in Terminologue is simply a file somewhere in the file system which SQLite opens and closes as and when it needs.

terminologue.js

Terminologue's backend can be started (among other ways) by running node terminologue.js from the terminal or command prompt. The contents of the JavaScript file terminologue.js is interpreted and executed by Node.js. The file tells Node.js to do a couple of things:

  1. It creates an Express application object called app.

  2. It uses methods such as app.post() and app.get() to add to this object a large number of handlers for the various URL end-points that a user might hit. A handler is a JavaScript function which Node.js executes when an HTTP request arrives at the server. Usually, a handler processes the data that came with the request and sends something back, for example a web page or a JSON object.

  3. Finally, at the end of the file, it calls app.listen(). This tells Node.js to start listening for incoming HTTP requests. From this moment, each time a HTTP request arrives at the server which matches one of the end-points created in step 2 above, Node.js executes its handler. Node.js patiently keeps listening and executing handlers until the application is terminated.

Obviously, each handler is different, but they typically do things like:

  • Read some data from the HTTP request by inspecting properties of the req object.

  • Open a connection to a termbase (a termbase in Terminologue is an SQLite database) by calling ops.getDB().

  • Find out whether the client is logged in and has access to the termbase, by calling ops.verifyLoginAndTermbaseAccess() or something similar.

  • Read or write some data from/into a termbase (= an SQLite database) by calling methods such as ops.entryRead(), ops.entrySave() and many others.

  • Close the connection to an SQLite database by calling db.close().

  • Send a response to the client, either as a JSON object (by calling res.json()) or a HTML page. If the handler is sending a HTML page, it calls res.render(). This hands control over to the EJS templating engine which grabs one of the HTML templates in the views directory (the files have the extension .ejs), executes any server-side code in the template (= anything between <% and %>) and sends the result to the client.

ops.js

Most handlers in terminologue.js call functions from the ops object, which is defined in the file ops.js. This file contains most of the low-level code which manipulates rows and columns in the databases. If we were using a separate database server instead of SQLite, most of this code would be in stored procedures. But we're using SQLite, and there is no such thing as stored procedures in SQLite, so we have ops.js.

The file ops.js makes a large number of functions available. Pretty much all the functions are asynchronous, they don't return any values. Instead, they take a callback function as one of their arguments and, when they have done their work, they execute this callback to hand control back to the HTTP handler in terminologue.js. Passing callbacks around (instead of returning values) is how these things are done in Node.js.

When an ops function reads from or writes into an SQLite database, the database is usually represented there as an object called db, which arrived as an argument from a terminologue.js handler. This object has methods such as db.run() and db.get() which take SQL statements and execute them on the database. These methods are asynchronous too, and we return from them through callbacks. Therefore, much of the server-side code in Terminologue has multiple levels of embedding callbacks inside callbacks inside more callbacks. Again, this is the normal pattern of doing things in Node.js.

This concludes our brief introduction to Terminologue's server-side code. We now turn our attention to the client-side code.

Screenful

All of the HTML pages we serve to the client are located in the website/views directory. Once the web page has arrived at the client's computer and has loaded in the client's web browser, we delegate most of the client-side functionality to the Screenful library.

Screenful gives us several page types which we make use of in Terminologue. For example:

  • The Screenful.Login page type is a single-page application which takes care of the login process.

  • The Screenful.Make page type is a single-page application with which a user can interact to create a new database. We use it on Terminologue to manage the process of creating a new termbase.

  • The Screenful.Navigator page type is a single-page application with a list of entries on the left-hand side and a space for viewing and editing an entry on the right-hand side. Terminologue uses this page page type as its main termbase editing screen (the screen that terminologists spend most of their time staring at).

  • The Screenful.Editor page type is a single-page application where you can edit an individual entry. It comes with buttons for opening, saving, deleting and so on. We use it on the right-hand side of the termbase editing screen (where it's embedded in an IFRAME) as well as in a couple of other places in Terminologue.

Each Terminologue web page declares which page type it is by including the relevant JavaScript and CSS files. For example, Terminologue's login page (website/views/sitewide/login.ejs) declares that it is a page of type Screenful.Login like this:

<script type="text/javascript" src="../libs/screenful/screenful-login.js"></script>
<link type="text/css" rel="stylesheet" href="../libs/screenful/screenful-login.css" />

It then supplies these additional parameters which tell Screenful (i) which URL it should send the login request to, and (ii) where it should redirect the user if the login is successful:

<script type="text/javascript">
  Screenful.Login.loginUrl="../login.json";
  Screenful.Login.redirectUrl="<%=redirectUrl%>";
</script>

The AJAX request which Screenful sends from the client to our server, and the response our server sends back to the client, is documented in Screenful. For example, the client sends a request like this to Screenful.Login.loginUrl, telling us that the user someone@example.com wishes to log in:

{
  "email": "someone@example.com",
  "password": "Hzwe86R!"
}

Our server may respond like this, which will prompt Screenful to redirect the user Screenful.Login.redirectUrl.

{
  "success": true
}

Or our server may respond like this, which will prompt Screenful to tell the user that the log in has failed and give him/her a chance to try again:

{
  "success": false
}

This is how Screenful works and this is how we use it everywhere in Terminologue, even for very complicated page types such as the termbase editing screen. We always declare that a particular web page is of a certain Screenful page type and then we make sure that we have end-points for the various server-side hookups which that page type needs.

Terminologue's copy of Screenful is located in website/libs/screenful. You should never edit anything in that directory. If you need to make changes to Screenful, consider sending a pull request to Screenful's repository instead.

Editing the entries: fy.js

One of the most complicated chunks of client-side JavaScript code we have in Terminologue is the code that deals with editing an individual terminological entry. Its output is shown on the main editing screen, after the user clicks the 'Edit' button, as a complex HTML form with tabs on top (DOM, TRM, etc.).

This JavaScript code lives in the file website/libs/fy/fy.js and the HTML it outputs is formatted with a stylesheet in the file website/libs/fy/fy.css. It contains two main functions:

  • Fy.render() which takes a terminological entry in JSON (which it has obtained from a termbase on the server) and renders it on screen as an HTML form which the user can then interact with. Pretty much all of the HTML you see on the right-hand side of the editing screen is the output of this function.

  • Fy.harvest() which takes the current state of the HTML form and "harvests" it into a JSON object ready to be saved into a termbase on the server.

The functions Fy.render() and Fy.harvest() are called by Screenful (more specifically, by the Screenful.Editor page type) as and when the user has indicated (for example by clicking a button) that he/she wants to open an entry, save an entry and so on.

Pretty-printing the entries

Another fairly complicated chunk of JavaScript code is the code that deals with formatting or "pretty-printing" the terminological entries. There are three places where this happens:

  • On the left-hand side of the editing screen where entries are listed. Each entry is pretty-printed here in abbreviated form.

  • On the right-hand side of the editing screen where an individual entry is pretty-printed in full form, with all details. The user can click the 'Edit' button to switch between viewing the pretty-printed entry or editing it with fy.js.

  • In the termbase's public interface (if the termbase is publicly visible) where entries are shown in their full form with all details, but with some minor differences from how they're shown in the editing interface.

This code lives in the website/widgets directory:

  • pretty-small.js and pretty-small.css are for pretty-printing in the entry list on the left-hand side of the editing screen.

  • pretty-large.js and pretty-large.css are for pretty-printing on the right-hand side of the editing screen.

  • pretty-public.js and pretty-public.css are for pretty-printing in the public interface of a termbase.

Each JavaScript file here contains a function called entry() which takes a terminological entry in JSON (which it has obtained from a termbase on the server) and outputs HTML. In pretty-small.js and pretty-large.js, the entry() function is executed client-side by Screenful every time it needs to render an entry on screen. In pretty-public.js the entry() function is executed client-side by Node.js and the output is sent to the client as part of a HTML page.

Conclusion

OK, that's probably enough detail for now. This document has hopefully given you a high-level overview of (i) Terminologue's server-side code, and (ii) some of the more complicated pieces of Terminologue's client-side code.

Gaois

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